How to confirm EFU installation seal? Equipment drawings, installation conditions and acceptance methods

Failure of the EFU installation seal is rarely due to poor quality of the gasket itself. The more common situations are: the tightening method of the sealing surface is not marked on the drawing, the flatness of the installation frame is exceeded, or the bolt tightening sequence is incorrect, causing the box to deform, and the compression amount of the sealing strip is either sufficient or insufficient. These problems may not necessarily appear as visible gaps immediately after installation, but the airflow will bypass the location of insufficient compression, and no matter how efficient the filter is, it cannot prevent unfiltered air from being directly mixed into the supply air. To confirm that the EFU installation is sealed, you need to string together the three links of drawing marking, installation conditions, and acceptance methods instead of going to the site to feel for air leakage. Aili Industrial's 70mm ultra-thin EFU supports customization of side air inlet/outlet and flange interfaces. The sealing structure is marked with the compression method and compression amount requirements in the confirmation drawing, which facilitates the equipment factory to complete the sealing verification at the drawing stage.

Equipment drawings: sealing surface, compression method and compression amount should be clearly marked

The starting point for confirmation of EFU installation seal is the drawing. Three things need to be marked on the equipment drawing: where the sealing surface is, how to compress it, and what the amount of compression is.。

The sealing surface is the interface between the EFU box and the equipment mounting frame or sheet metal. The flatness and surface condition of this interface determine whether the gasket can be compressed evenly. The flatness requirements of the sealing surface should be marked on the equipment drawings instead of just giving an outline dimension. If the mounting frame is a welded part, the post-weld deformation will cause the sealing surface to appear wavy, and the sealing gasket will be under-compressed at the low point, and the airflow will bypass there.

There are usually two compression methods: mechanical compression and liquid tank sealing. There are clear specification references for the thickness and compression ratio of mechanical compression seals. Relevant construction acceptance specifications require that when the high-efficiency filter adopts a mechanical seal, the sealing gasket thickness should be 6-8mm. After installation, the gasket compression should be uniform, with a compression rate of 25%-50%. This compression rate range is the premise for the gasket to play a rebound sealing role - too little compression, and the gasket will not fit the pressure; too much compression, and the gasket will be excessively deformed and lose its resilience, making it more likely to leak after long-term operation.

Liquid tank sealing requires marking the knife edge insertion depth and liquid tank level on the drawing. The tank frame should be installed horizontally without leakage. The height of the sealing liquid in the tank should be 2/3 of the tank depth. If the EFU on the equipment side adopts liquid tank sealing, the position of the knife edge and the installation space of the liquid tank need to be given on the equipment drawing, not just the 'leaving a tank' indication.

In the EFU confirmation drawing, Aili Industry marks the sealing surface position, gasket type and compression requirements according to the equipment installation surface. The sealing structure of the ultra-thin model is listed together with the position of the box fixed point to prevent the sealing surface from being deformed by the pretightening force of the fixing bolts.

Installation conditions: frame flatness, fixing sequence and peripheral clearance

After the drawing is confirmed, the installation conditions determine whether the sealing can be achieved according to the drawing. Three conditions need to be checked before the EFU is put in place.

Flatness of mounting frame . The EFU box itself is rigid, but the thin-walled box will produce local deformation under the bolt pretightening force. If the surface of the installation frame is uneven, when the box is pulled toward the frame by the bolts, the compression amount of the gasket will be different at different locations. Before installation, use a knife-edge ruler or ruler to check the flatness of the frame. Any out-of-tolerance locations need to be trimmed or shimmed instead of tightening the bolts.

Fixed order . For multi-bolt fixed EFU, the tightening sequence directly affects the compression uniformity of the gasket. Starting from one end and tightening one by one, the box will be pulled to one side and the gasket at the other end will not be compressed enough. A more pragmatic approach is to tighten symmetrically and in stages from the middle to both ends, each time tightening to a part of the rated torque, so that the gasket is gradually and evenly compressed. Relevant specifications also require that the entire unit remains flat after installation, and there should be reliable sealing measures between the fan box and the filter, and between the filter unit and the installation frame.

Peripheral clearance . After the EFU is installed into the device, there may be a design gap or installation deviation between the box and the installation frame. If these gaps fall outside the sealing path, they need to be filled with sealant or sealing strips; if they fall on the sealing path, the width and compression of the gasket need to be able to cover this gap. The actual size of the gap should be measured before installation, rather than assuming that 'the gasket is thick enough to hold it down.' For the relationship between the mounting hole position and the sealing surface, please refer toHow to confirm the mounting hole position of customized EFU? datum, tolerance, fixing and sealing surface inspection .Fixing and sealing surface verification methods in

Acceptance method: light transmission inspection, compression measurement and scanning leak detection

After the seal installation is completed, the acceptance inspection needs to be able to judge 'whether there is a bypass', instead of just looking at 'it looks tight'.

Light transmission inspection is suitable for mechanical compression seals. In a dark environment, use a light source to illuminate the sealing surface from the air outlet side of the EFU, and observe whether there is light coming through from the air inlet side. Translucent locations correspond to areas where the gasket is undercompressed or has gaps. This method is simple, but has limited sensitivity to small gaps and is suitable as a preliminary screening.

Compression measurement is more direct. Before tightening the bolts, place soft lead wires or special compression measurement pieces at several representative positions of the sealing gasket. After tightening, take out the thickness changes and calculate whether the compression rate falls within the range of 25%-50%. The measuring points should cover the midpoints and corners of the four sides of the sealing surface, where uneven compression is most likely to occur.

Scanning for leaks is the final confirmation of acceptance. For equipment-side EFUs with cleanliness requirements, the sealing interface should be scanned for leaks after installation to confirm that there is no unfiltered air bypass. The scanning method can refer to the common practice of high-efficiency filter leak detection, and use a particle counter to detect the periphery of the sealing surface while the EFU is running. Relevant specifications require that the surrounding areas and interfaces of the high-efficiency filter should be tight and leak-proof after installation, and scanning and leak detection should be performed before debugging. If the scan finds that the local count is too high, the seal at that location needs to be re-tightened or filled with glue.

In the EFU supply, Aili Industrial can mark the sealing structure and compression method according to the equipment drawings. The compression amount of the sealing gasket is measured during the assembly of the prototype or the first unit, and the scanned leak detection data and confirmation drawings are filed together as a comparison benchmark for batch sealing configurations.

Misunderstandings to avoid

It should be avoided to only draw the position of the gasket without marking the compression amount requirement on the drawing. It should be avoided to tighten the EFU bolts directly without confirming the flatness of the frame. It should be avoided to tighten the gasket sequentially from one end to cause uneven compression. It should be avoided to only replace the scanning leak detection with light transmission inspection. It should be avoided to perform the seal acceptance when the EFU is not running. The core of EFU installation seal confirmation is not 'whether the sealing gasket is placed', but the drawing marking, installation conditions and acceptance method to form a measurable and traceable closed loop.

Related questions and answers

What is the compression rate of EFU gasket?
The reference range of compression ratio of mechanical compression seal is 25%-50%, and the thickness of sealing gasket is usually 6-8mm. If the compression rate is lower than the lower limit, the sealing gasket does not have enough fitting pressure; if it is higher than the upper limit, the sealing gasket is excessively deformed and loses rebound, and it is easy to leak after long-term operation. The specific value should be confirmed according to the gasket material and supplier's requirements.

If no light leakage was found during the light transmission inspection, do I still need to scan for leaks?
Recommended to do. Translucent inspection has limited sensitivity to tiny gaps, and bypass of the EFU sealing surface may occur at micron-level gaps. For equipment-side applications with cleanliness level requirements, scanning and leak detection is the final means to confirm the integrity of the seal, and should be completed and recorded before commissioning.

The EFU is installed on the equipment sheet metal. How to deal with uneven sheet metal?
First measure the range and degree of flatness deviation. Local low points can be transitioned with thin gaskets, and large uneven areas require trimming the frame or adding transition mounting plates. It is not recommended to force the flattening by increasing the bolt torque, as this will cause pre-deformation of the box and affect the filter seal and air duct shape.

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Key points for selection and acceptance inspection

Aili Industrial EFU selection and procurement support

Aili Industrial's 70mm ultra-thin EFU supports mechanical compression and flange interface customization. The sealing surface position, gasket type and compression amount requirements are marked on the confirmation diagram. The equipment factory can submit frame flatness conditions and sealing method requirements based on the equipment installation surface. Aili Industrial will match the sealing structure and fixed point layout accordingly. The compression amount will be measured during the prototype stage and a scanning leak detection record will be completed.

Learn about Aili Industrial EFU products and customized configurations. Check out the compact models.70mm ultra-thin EFU , the entire machine structure can be viewedEFU equipment fan filter unit , non-standard interface and sealing structure can be viewedCustom EFU . Please submit equipment installation surface drawings, sealing methods and cleanliness requirements to facilitate confirmation of sealing configuration and acceptance methods.